In late years, attention has be riveted to composite oxide materials as ferroelectric materials, oxide magnetic materials, oxide semiconductor materials, nonlinear optical materials, insulating materials, transparent electrode materials, low dielectric materials and oxide superconducting materials. Such a composite oxide material is comprised of various blocks having different in composition, lattice constant or crystallographic structure, layered one on top of another. This structural peculiarity has made it difficult to make up a composite oxide material satisfactory in crystallinity with the block epitaxially grown one on top of another.
A Cu group superconducting material that has attracted attention as an oxide superconducting material has a crystallographic structure in which a charge supply block and a superconducting block are formed one on top of another so as to be oriented in a direction of the crystallographic c-axis. Realizing a Cu group superconducting material excellent in superconducting properties requires realizing a crystallographic structure that is excellent in the c-axial orientation of both a charge supply and a superconducting block. However, large lattice mismatch between the charge supply and superconducting block makes it difficult to cause these block to grow epitaxially one on top of another. Indeed, it has been believed difficult to cause those blocks to so grow epitaxially by any method other than high-pressure synthesis and post annealing in Tl vapor.
Manufacturing a Cu group superconducting material by high pressure synthesis or Tl or Hg post annealing, however, has presented such problems as being costly, making it hard to yield thin films large in area, inadequacy for volume production and also toxicological problems. Further, it has entailed difficulties in controlling the basic unit cell structure as desired to make the material reproducibly and has required a high temperature and long term post annealing heat treatment in an oxidizing or reducing atmosphere for the material made. Moreover, the need for a high temperature in the process of manufacture has required the crystalline substrate on which a thin crystalline film satisfactory in the c-axial orientation is to be formed to be only a limited material that can withstand the high temperature.
These problems in the prior art mentioned as for Cu group superconducting materials commonly apply to composite oxide materials in general.
With the aforementioned problems born in mind, it is accordingly an object of the present invention to provide a method and an apparatus which permit making a thin film of composite oxide with satisfactory crystallinity easily and at a low temperature, with the capability of controlling the basic unit cell structure as desired, without necessitating either high temperature or high pressure and without the need for a post annealing. It is also an object of the present invention to provide a thin film of composite oxide made by such a method or an apparatus.